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Extension > Garden > Yard and Garden > Outdoor-indoor geranium culture

Outdoor-indoor geranium culture

Deborah L. Brown, Professor, Department of Horticulture Science
Harold F. Wilkins, Retired Professor, Department of Horticulture Science

The garden geranium is a favorite outdoor-indoor plant. It belongs to the genus Pelargonium which means “stork” in Latin. This plant has a long, slender fruit capsule that resembles a stork’s bill. There are over 200 Pelargonium species and many well-known hybrids. Most species originated in South Africa. The common garden geranium is Pelargonium hortorum.

Pelargonium 'Cherry Orbit'

Pelargonium 'Cherry Orbit,' a seed-grown hybrid geranium

Few plants offer such variation in flower color, growth habit, leaf pattern, and scent. Geranium flowers come in white, pink, salmon, red, fuchsia, lavender, and bi-colors. There are double flower types and old-fashioned singles. Growth habits range from trailing vine types to upright garden forms. Leaves may be nearly circular or deeply segmented and lacy. They can be green, green and white, or patterned with combinations of reds, yellows, and oranges. Although the flowers have an unpleasant odor, there are scented-leaf geraniums that are very pleasant. Aromas include lemon, orange, lime, peppermint, pineapple, nutmeg, rose, and many others.

lacy-leaved, scented geraniums

Two examples of lacy-leaved, scented geraniums.

Martha or Lady Washington geraniums (Pelargonium domesticum) have the brightest flowers, with colors from purple black to vivid yellow. They do not make good garden plants in Minnesota, however, because they must have cool (50° to 60°F) night temperatures to blossom. This means they will bloom only in early summer and in autumn, not July or August.

Though geraniums have traditionally been grown from cuttings in greenhouses, many are now grown from seed that is planted in small "plugs" then grown on before being sold. These hybrid seed geraniums may not be in full flower when you buy them, but they often outperform geraniums grown from cuttings, especially in late summer and early autumn.

Seed-grown geraniums are a welcome addition to any sunny garden. Their color range is similar to that of cultivars propagated from cuttings. Elite, Maverick, Multibloom, Orbit, Pinto, and Ringo are just some of the color series of seed geraniums that are available.

Outdoor geranium culture

Wait to plant geraniums outdoors until frost danger has passed and the soil temperature reaches 60°F. Choose a site with lots of sunlight, ideally eight hours or better. With less sun, the plants will bloom sparsely. Soil should be open and porous to allow for good water drainage, oxygen penetration, and healthy root growth. A heavy soil will benefit from the incorporation of several inches of peat, compost, or perlite before planting geraniums. Do not use manure or vermiculite. Sandy soil will also be measurably improved by the addition of organic matter.

Geraniums will not bloom well if they are overfertilized. Two pounds of 10-10-10 dry fertilizer or 4 pounds of 5-10-5 dry fertilizer for 100 square feet can be incorporated into the soil at planting. A half-rate application of this dry fertilizer can be spread at mid-season in July. Water these dry fertilizers into the soil. An alternate fertilizer scheme is to use 2 level teaspoons of water-soluble 20-20-20 fertilizer in 1 gallon of water, applied every three weeks. Use either dry or water-soluble fertilizer methods, but don't use both or you will overfeed the plants.

When you plant, make an irrigation furrow or dike around the plants to serve as a reservoir for summer watering.

Water geraniums thoroughly, but allow the soil to dry between waterings to avoid root rot. Do not allow the plants to wilt, however. Cycles of wilting, followed by a heavy watering, cause leaf drop and result in poor growth.

Remove faded flowers and dry leaves from the plants. These attract Botrytis fungus which attacks leaves and young buds. Protective fungicide sprays may be necessary during periods of cool, moist weather. Check your garden center for products labeled for use on geraniums. Fortunately, insects are generally not a problem.

Geraniums are attractive in outdoor planters and tubs. The soil in these containers becomes warm from the sun, so it's important to water regularly. Planters and tubs must have drain holes so moisture won't be trapped in the bottom, causing roots to rot. Hanging baskets with trailing geraniums are also attractive, provided they are kept in a sunny location, out of damaging wind.

If you have a bright location indoors, you can bring your geraniums inside and keep them growing as houseplants until it's warm enough to put them out the following spring.

The practice of storing geraniums in the basement over the winter works better with cold, damp basements than it does with dry, warmer, modern basements. Minnesota has only about 130 frost-free days, and half the summer could go by waiting for poorly overwintered plants to bloom again.

Indoor geranium culture

Prospects for success when growing geraniums indoors depend largely on having enough light to promote flowering. Geraniums thrive in full sunlight, but in Minnesota the shortest winter day is only about eight hours, and frequently there is little sun during that time. In the absence of a bright, sunny window, supplemental fluorescent tube lighting kept 10 to 12 inches from the plants will help growth. Fluorescent lights can be used from 6 p.m. to 10 p.m. to supplement natural light.

Overwatering will cause geraniums to rot. Feel the soil to determine when to water. If it's dry to the touch, water thoroughly. If it feels moist and cool, don't water. Geraniums tolerate dry soil conditions better than excess moisture.

Geranium pots can be either clay or plastic, but must have drain holes. Saucers placed under the pots to collect water should be emptied a few minutes after watering. If a large, shallow pan is used to display several plants, gravel can be placed on the bottom. The evaporating water from the gravel surfaces will increase humidity.

In the home, geraniums do not require frequent fertilization. By potting young plants in a good soil mix (1 part soil, 1 sand, 1 peat), additional nutrition will not be required for two or three months. Water-soluble 20-20-20 can be used at the rate of 1 level teaspoon in 1 gallon of water. For plants that are kept indoors year-round, fertilize during growth periods only.

Geraniums thrive in a wide range of temperatures. Ideally, they should be grown at 65°F day and 55°F night temperatures. Often geraniums are grown at temperatures that are too warm. Many houses and apartments have radiators by the windows to compensate for heat loss. Thus, maintaining plants near a light source without overheating may be a problem. Avoid cold, drafty areas as well as hot, dry locations.

Indoor gardeners should prune or pinch their plants. Removing the growing point will produce a plant that is stocky and well-branched. Several vigorous stems may be allowed to form a shrub-like plant. Occasionally, geraniums are trained into the shape of a tree. To do this, allow a single stem to develop and remove all side shoots. Use a stake for support. When the desired height is reached, remove the top growing point. Allow only the upper side buds to form shoots. With time and shearing, these shoots will form the shape of a tree.

Propagation

Geraniums can be reproduced easily from cuttings. The cuttings can be taken any time of year, but root most readily in spring or summer. Start with disease-free, vigorous plants. Take short, terminal stem sections two to three inches long. Place the cuttings in vermiculite or any well-drained sterile soil mix, rather than in water. If wilting is a problem, place a plastic bag over the pot. When roots are evident, slowly open the bag and move the plant into full sunlight over a period of days.

Geranium cuttings

Geranium cuttings can be propagated by rooting them in vermiculite. Both pots should have drainage holes. The smaller clay pot is a water reservoir, so it must be corked tightly.

well-rooted geranium cutting

This well-rooted geranium cutting is ready for planting.

Seeds may be started indoors in mid-January in flats of potting medium kept at 75°F during germination. Grow seedlings under fluorescent lights until they're ready to be transplanted outdoors. Keep lights only three or four inches above the growing plants and leave them lit for 16 to 20 hours daily.

Geraniums have been garden favorites for a long time, and with good reason. With proper care they can add color and beauty to sunny spaces both outdoors and in the home.

WW-01118 Reviewed 2009
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